This invention relates to an apparatus for forming thin films and more particularly to such an apparatus for forming protective thin film layers.
In general, a magnetic memory device is produced by first forming a magnetic layer on a substrate for storing data and then forming a protective layer on the magnetic layer for protecting the magnetic layer from the external environment.
For forming protective layers for a magnetic memory device having magnetic layers on both surfaces, it has been known to use an apparatus for forming thin films by sputtering and to form protective layers at the same time on both surfaces of the substrate with magnetic layers formed thereon.
When data are written on or read from such a magnetic memory device, a magnetic head is positioned opposite to its magnetic layer with a protective layer in between. Since the read/write characteristic of a magnetic head depends on the distance separating it from the magnetic layer, it is necessary to reduce this distance as much as possible in order to improve the magnetic recording characteristic of a magnetic recording system. It is for this reason that there is an increasing demand for thinner protective films.
Protective films produced by conventional sputtering methods have problems in that their characteristics such as resistance against voltage, resistance against corrosion and resistance against wears deteriorate if the thickness is less than about 10 nm, or about 12.5 nm as a practical matter, and hence that the film can no longer fully serve as a protective layer.